Methanol is readily producible from coal and other raw materials by the use of well-known commercial processes. For example, synthesis gas, i.e., a gaseous mixture comprising hydrogen and at least one carbon oxide, in particular carbon monoxide, can be obtained by the partial combustion or gasification of any organic material such as coal, other hydrocarbons, carbohydrates and the like. Synthesis gas can be manufactured into methanol by a well known heterogeneous catalytic reaction using catalysts such as copper-zinc oxide and other copper-based catalysts.
Methanol is frequently used as a feedstock to produce other compounds. For example, "Hydrocarbons from Methanol" by Clarence D. Chang, published by Marcel Dekker, Inc. N.Y. (1983) presents a survey and summary of the technology described by its title. Chang discusses methanol to olefin conversion in the presence of molecular sieves at pages 21-26. Olefin production from methanol has been the subject of a number of patents. For example, see U.S. Pat. Nos. 4,079,095; 4,238,631; 4,328,384; 4,423,274; and 4,499,327. Methanol to olefin conversion is also discussed in commonly assigned U.S. patent applications Ser. Nos. 070,579, 070,574, 070,575 and 070,578, each filed July 7, 1987. Each of the patents and patent applications identified above are incorporated in its entirety by reference herein.
While olefins, in particular light olefins, are often quite valuable, continuing efforts are needed to reduce the cost of production. Recently, these efforts have centered around increasing the selectivity of various catalysts toward converting methanol into the desired olefins. Various processing and catalyst modifications have been suggested, e.g., see the above-noted patents and publication.
However, even though improved selectivities have been achieved, a certain amount of undesired products, e.g., paraffins, heavier olefins and the like, is produced. These undesired products are often discarded or used in applications of reduced value, thereby increasing the feedstock cost per unit of olefins produced.
In addition, conventional processes to produce synthesis gas methanol from synthesis gas and olefins from methanol each involve separate separation steps, e.g., in order to provide pure or specification grade product. These separation steps are relatively capital and labor intensive, and add substantially to the manufacturing costs involved in producing such products. Clearly it would be advantageous to provide a process useful to effectively and economically produce olefins.